Amorphous calcium phosphate (ACP), a key precursor in the biological formation of hydroxyapatite (HAP), has received less attention as a dental material than crystalline calcium phosphates (CaPs). ACP, however, has two properties that justify its utilization as a possible remineralizing agent: it is one of the most soluble of all the biologically important CaPs, and it exhibits the most rapid conversion to HAP. Recently we developed unique polymeric dental composites/sealants that utilized these properties of ACP to remineralize bovine enamel lesions in vitro. However, as currently formulated, these ACP composites have relatively low mechanical strength and adhesiveness to teeth. Such shortcomings may limit their wider utilization in dentistry. The objectives of this proposal are (1) to develop effective remineralizing dental composites based on ACP that will have optimal mechanical and adhesive properties while maintaining sustained release of Ca and PO4 ions, and (2) to enhance our understanding of the remineralizing behavior of these ACP-based materials, especially the major factors that control Ca and PO4 ion release and redeposition into HAP. To accomplish these objectives we propose to: l] prepare ACP fillers with structurally incorporated silica, zirconia, and/or titania; 2] develop surface- modified hybrid ACP fillers amenable to treatment by silane coupling agents; 3] explore the effects of resin composition on the, mechanical and physicochemical properties of ACP-composites, and 4] evaluate the effects of bifunctional methacrylates on the adhesion of the composites to tooth substrates. It is expected that this research will both advance our fimdamenta1 understanding of these novel bioactive composites and eventually lead to clinically useful products. The extended, time-releasing nature of these ACP based polymeric materials should be especially useful in dental sealant and adhesive applications for preventing demineralization or promoting remineralization.